Effect of Kruppel‐like factor 4 on PTZ‐induced acute seizure mice

Abstract Kruppel‐like factor 4 (Klf4) is a transcription factor that is involved in neuronal regeneration and the development of glutamatergic systems. However, it is unknown whether Klf4 is involved in acute seizure. To investigate the potential role of Klf4 in pentylenetetrazol (PTZ)‐induced seizure, western blotting, immunofluorescence, behaviour test and electrophysiology were conducted in this study. We found that Klf4 protein and mRNA expression were increased in both the hippocampus (HP) and prefrontal cortex (PFC) after PTZ‐induced seizure in mice. HP‐specific knockout (KO) of Klf4 in mice decreased protein expression of Klf4 and the down‐stream Klf4 target tumour protein 53 (TP53/P53). These molecular changes are accompanied by increased seizure latency, reduced immobility time in the forced swimming test and tail suspension test. Reduced hippocampal protein levels for synaptic proteins, including glutamate receptor 1 (GRIA1/GLUA1) and postsynaptic density protein 95 (DLG4/PSD95), were also observed after Klf4‐KO, while increased mRNA levels of complement proteins were observed for complement component 1q subcomponent A (C1qa), complement component 1q subcomponent B (C1qb), complement component 1q subcomponent C (C1qc), complement component 3 (C3), complement component 4A (C4a) and complement component 4B (C4b). Moreover, c‐Fos expression induced by PTZ was reduced by hippocampal conditional KO of Klf4. Electrophysiology showed that PTZ‐induced action potential frequency was decreased by overexpression of Klf4. In conclusion, these findings suggest that Klf4 plays an important role in regulating PTZ‐induced seizures and therefore constitutes a new molecular target that should be explored for the development of antiepileptic drugs.


| INTRODUC TI ON
Seizure disorders are common, chronic and serious neurological disorders throughout the world. 1 Although there are many therapeutic methods to treat seizure disorders, they are not effective in many patients, and some patients are completely resistant to all current treatments.Moreover, most anticonvulsants present a variety of side effects that limit the effective use in many patients.
Additionally, these conditions often present early in life and early exposure to anticonvulsants may be associated with the increased risk of developing psychiatric disorders, including autism spectrum disorder. 2Some anticonvulsants may also worsen other psychiatric symptoms, inducing manic symptoms. 3,4Consequently, the development of new molecular targets for antiepileptic drugs is a critical need in the treatment of seizure disorders.
It is well known that Klf4 induces pluripotency in stem cells (iPSCs). 5Klf4, a zinc finger-containing transcription factor, has been reported to play roles in stem cell differentiation, 6 cancer 7,8 and atherosclerosis. 9Klf4 is highly expressed in the cerebral cortex, hippocampus (HP) and hypothalamus 10,11 and has important developmental roles in regulating glutamatergic function. 12In the central nervous system (CNS), Klf4 has been implicated in neuron regeneration, 13,14 brain tumour formation, 15 neuronal apoptosis, 16 and the pathophysiology of traumatic brain injury 17 and Alzheimer's disease. 18,19Given the apparent broad role of Klf4 in brain plasticity 20 and neurodegenerative disorders, it might also be thought that Klf4 would influence general brain excitability and therefore have a role in seizure disorders.Nonetheless, our understanding of the involvement of Klf4 in seizure disorders remains unclear.
P53 is a downstream mediator of Klf4 actions that are important in amyloid β-protein 19 or Traumatic brain injury (TBI)-induced neuroinflammation. 21Whether a result of this neuroinflammatory cascade or other actions of Klf4, changes in brain excitability involving p53 are unclear.Activated p53 occurs in pilocarpine-induced drug resistant epilepsy, 22 pentylenetetrazol (PTZ)-induced seizures 23 and post-traumatic epilepsy (PTE) animal brains. 24PTZ-induced seizures in rats. 23This likely results from increased neuronal activity as the neuronal marker (NeuN) c-Fos is also increased by PTZ, while anticonvulsant treatments decrease this elevation in c-Fos expression. 16,25,26 is an important brain region related to seizures.c-Fos expression is increased by convulsants, and decreased by anticonvulsants, in the HP and PFC. 25 In this study, we investigated the anticonvulsant effect of Klf4 in PTZ-induced acute seizures in mice, along with behavioural and molecular characterization of the effect of conditional hippocampal Klf4-KO on PTZ-induced seizures.The effect of overexpression of the Klf4 on PTZ-treated hippocampal neuronal excitability was also determined using whole-cell current-clamp recordings.

| Effects of conditional hippocampal Klf4-KO on PTZ-induced acute seizure and the expression of Klf4, P53 and c-Fos
As shown in Figure 6, conditional hippocampal Klf4-KO increased the PTZ-induced seizure score (Figure 6B, p < 0.01), but had no effect on seizure latency (Figure 6A).Tukey comparisons showed that PTZ increased p53 protein expression (p < 0.05), the effect was reversed by conditional hippocampal Klf4-KO (p < 0.01).To explore the effect of PTZ on the interaction between proteins in the HP, co-immunoprecipitation was performed.Figure 6G shows co-immunoprecipitation results for Klf4 and p53.There was a direct interaction between Klf4 and p53 in the HP, which was increased by PTZ.

| Effects of overexpression of Klf4 on action potential frequency of hippocampal pyramidal neurons
As Figure 7A-C shows that viral over-expression of Klf4 alone had no effect on action potential (AP) frequency.PTZ increased AP frequency in cells from control (LV-EGFP) mice (two-way ANOVA: F (3, 36) = 31.166,p < 0.001; p < 0.001 vs. saline) and this effect was reduced by overexpression of Klf4 (p < 0.01 vs. LV-EGFP mice treated with PTZ).There was no significant difference between salinetreated LV-EGFP cells and PTZ-treated LV-Klf4 treated cells on AP frequency.

| DISCUSS ION
This study revealed that the transcription factor Klf4 was regulated following PTZ-induced acute seizures in mice.Glutamatergic stimulation induces swift upregulation of Klf4 expression in cultured neurons and Klf4 overexpression activated caspase-3 after treatment with NMDA (10 μM). 12Consistent with these overall roles, the present experiments demonstrate that Klf4 plays a protective role in the acute seizure.In addition, viral-mediated over-expression of Klf4 gene expression in vitro also increased seizure latency.Thus, both approaches are consistent with the role of Klf4 in reducing seizure susceptibility.
To further explore the role of the Klf4 in the epilepsy, conditional hippocampal Klf4-KO mice were constructed, and behaviour and molecular characterization were performed.Klf4-KO mice did not affect the behaviours in the Y-maze and OFT.There was a selective effect upon depressive-like behaviour where Klf4-KO mice exhibited reduced immobility time in the FST and TST.The reason may be related to changes in neural excitability in Klf4-KO mice under some conditions.Repeated electroconvulsive therapy decreases immobility time in the FST, 27,28 so that a similar change in hippocampal excitability may occur here.Although there were no differences at baseline, PTZ-induced seizure activity was reduced.Supporting this relationship between depressive phenotypes and hippocampal excitability, in a genetic absence epilepsy model in Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats decreases in immobility time in the FST are observed. 29otein expression levels of neuronal and glial markers including NeuN, GFAP and Iba1 in HP were detected through western blotting.
GFAP and Iba1 were increased in the Klf4-KO mice.Activated glia also produce cytokines, produce neuronal hyperexcitability and inflammation that may contribute to the pathogenesis of epilepsy. 30,31A recent study reported that overexpression of Klf4 confers vascular protection via reducing cerebral vascular endothelial inflammation. 32Although some evidence has shown that Klf4 plays a critical role in CNS function and susceptibility to some neurological disorders, the specific mechanisms are still obscure.Importantly, Klf4 contributes to microgliamediated neuroinflammation in Alzheimer's disease. 19,33However, another study reported that LPS stimulation increased Klf4 expression in microglial cells in a time and dose-dependent manner.Klf4 resulted in decreased levels of the pro-inflammatory cytokines such as TNFα, MCP-1, IL-6 and IFN-gamma. 34,35The apparent inconsistency of these Further work needs to be done to show if changes in Klf4 are a cause or result of some of these inflammatory changes.
In the present study, synaptic proteins including GluA1, PSD95 and Synapsin1 were also detected by western blotting in the Klf4-KO mice.GluA1 and PSD95 were decreased in PTZ-treated mice, as in a previous study. 36That study reported that ICV injection of the four reprogramming factors Oct4, Sox2 c-MYC and Klf4 increases protein expression of PSD95, thereby reversing brain damage-induced synapse plasticity. 37These results indicated that Klf4 may play an important role in synaptic plasticity.
Protein levels of are not changed after Klf4-KO.Similar to what was observed here, activated microglia and complement cascade C1q signalling in the HP may contribute to synaptic loss in a mouse model of neuroinflammation induced by repeated LPS injections. 38Inflammation also decreases PSD95 in the HP. 39reover, complement mRNA expression was also tested by PCR here.These complement factors are mediators of inflammation, and also involved in the molecular mechanisms of epilepsy. 40In this study complement 1q (a, b and c), 1q3 and 1q4 (a and b) all were increased in Klf4-KO mice.The complement C3-C3aR pathway mediates microglia-astrocyte interactions following status epilepticus (SE) 41,42 reported that C4B (but not C3)-deficient mice exhibited increased susceptibility to seizures induced by PTZ and failed to upregulate the expression of multiple immediate early genes (IEGs) including Egrs1-4 and c-Fos.These findings suggest that seizure behaviour may be related to inflammation-related microglial and astrocytic activation and further affects synaptic protein changes.
In this study, conditional hippocampal Klf4-KO did not affect seizure latency.Viral-mediated overexpression of Klf4 in vitro did increase seizure latency.This may have to do with differences in circumstances.An acute seizure may increase Klf4 protein expression, 43 but chronic seizure may decrease Klf4 protein expression.Decreased Klf4 protein levels were found in a PTZ-kindling mouse model of epilepsy. 20In addition, in a small sample size clinical study expression of Oct4, Sox2, c-MYC and Klf4 genes was increased after initial electroconvulsive stimulation.Gene expression levels after treatment were significantly different from the initial gene expression. 44Our recent work found that Klf4 can exert sedative effects in pentobarbital-treated mice through modulation of p53 and the Stat3 pathway in the hypothalamus. 45Further study is needed to evaluate potential biphasic changes in Klf4 expression in the development of the seizure.
The western blotting study indicated that PTZ increased Klf4 expression, and the effect was reversed by Klf4-KO.Further examination of a potential downstream mediator of these effects showed that p53 was also increased by PTZ, and the effect was reversed by Klf4-KO.These results are consistent with a previous study which found that P53 was increased by PTZ treatment. 23P53 as a downstream mediator of Klf4 is well studied in inhibition of proliferation and tumour suppression. 46,47Elevated P53 levels have been reported in epilepsy animal models and the hippocampuis of epilespsy patients. 22,48In the present study, Klf4-KO regulated the Klf4-p53 pathway and increased seizure scores.Recently, some evidence showed a regulatory role of p53 in neuronal activity.Deletion of p53 protects neurons from stress and damage. 49,50It was also found that depletion of p53 attenuated cocaine-induced kindling behaviours and associated c-Fos immunoreactivity in the HP. 51In addition, consistent with this hypothesis, we found that Klf4-KO mice had increased p53 protein levels after PTZ treatment and PTZ increased interactions between Klf4 and p53 in the HP.These findings align with the results that the downregulation of p53 induced by Klf4 overexpression attenuated PTZ-induced excessive neuronal activities.
To a certain extent, all of these effects involve alterations in brain excitability, which were consistent with both the immunohistochemistry and electrophysiology experiments.In the c-Fos immunofluorescence study, in the DG of the HP and piriform cortex, PTZ was associated with increases in c-Fos positive neurons.These effects were reversed by overexpression of Klf4.Consistent with the above findings, these results indicate that alterations in neuronal activity (and neuronal excitability) in the HP may contribute to the anticonvulsant effects of Klf4 overexpression.These results are consistent with a previous report showing that PTZ affects the HP, 25 and that Klf4 is involved in the inhibition of c-Fos expression in the regions.
Consistent with the Western blotting and immunohistochemical studies, the electrophysiological study found that overexpression of Klf4 reverses the increases in AP frequency in hippocampal pyramidal cells produced by PTZ.
Reprogramming factors (Klf4) might be potential molecular targets for neurogenesis.Febrile seizures or SE may lead to transient upregulation of adult neurogenesis in the HP 52,53 and may have a role in later epileptogenesis.Moreover, acute PTZ-induced generalized tonic-clonic seizures were increased the number of proliferating cells in both the dentate gyrus and the subventricular zone.
Therefore, increased Klf4 after a single PTZ administration may be related to neurogenesis and neuroprotection.In terms of its relationship to chronic seizure, Klf4 protein expression and neurogenesis may involve more complex mechanisms.Further study is needed to evaluate the detailed mechanisms.
In summary, the results of this study suggest that Klf4 is increased in PTZ-induced seizures, and the mechanisms Klf4-p53 pathway may be involved in the observed behavioural outcomes.Inhibition of this pathway by hippocampal Klf4-KO exhibits proconvulsant effects.
Similarly, overexpression of Klf4 in vitro showed anticonvulsant effects as shown by reduced action potential frequencies.These findings suggest that Klf4 may constitute a novel molecular target for the development of anticonvulsive agents.However, this study has some limitations that should be addressed in future research.Klf4 anticonvulsant effects need to be further investigated, particularly under more chronic circumstances.

| Animals
Imprinting Control Region (ICR) strain male ICR mice (age: 6-8 weeks) were purchased from Jilin University (Changchun, China).Animals were housed in plastic cages (mice: 25.5 × 15 × 14 cm) and maintained in standard laboratory conditions (temperature: 23 ± 1°C, lights on and off: 07:00 and 19:00), with ad libitum access to food and water.All experiments were carried out in accordance with the Guide for Animal Experimentation of Jilin University and every effort was made to minimize any potential suffering experienced by the animals.

| Drugs
PTZ was purchased from Sigma-Aldrich (St. Louis, MO, USA).The drug was dissolved in sterile, pyrogen-free saline.Doses of PTZ (70 mg/kg) were selected based on previous studies. 7,25

| Experimental design
To investigate the effects of PTZ on Klf4 in mice and its related mechanisms, mice were divided into two groups: a control group

| Seizure latency after PTZ injection
Behavioural changes in the test subjects were monitored for 30 min after PTZ injection (65 mg/kg, ip).Seizure behaviour was categorized following the classification method outlined in our previous study 54  of righting.Additionally, the latencies for the onset of myoclonic jerks and clonic seizures were measured, with a maximum observation period of 30 min following the PTZ injection. 54Mice were survived 30 min after PTZ injection.

| Y-maze test
Y-maze test was performed following a previously outlined protocol. 55In summary, individual mice were introduced to one of the arms and given 8 min for unrestricted exploration.The alternation score (%) was computed using the following formula [(number of consecutive sets of three arm choices, each including all three arms)/ (total arm entriesa−2)] × 100.An arm entry was recorded when all four limbs of the mouse were inside an arm.

| Open field test
OFT was employed to assess locomotor and exploratory behaviours.Mice were individually placed in a black acrylic cylinder (diameter: 48.8 cm; height: 16 cm) divided into 19 equal squares by black lines.The horizontal and vertical locomotor activities of mice were recorded using a camera for a 6-min duration.Each animal was tested only once.Following the trial, the chamber was cleaned to avoid any impact on the results of subsequent experiments.Detailed experimental procedures can be found in previous reports. 56,575.3| Forced swimming test FST was carried out following the previously described method.58 Mice were placed in a cylindrical transparent plastic tank with a diameter of 11 cm and a depth of 25 cm, filled with water to a depth of approximately 10 cm, and maintained at a temperature of 25 ± 1°C. Af a 2-min adaptation period, the observation was initiated in an environment free from external disturbances.The immobility time of mice were observed during the last 4 min.The FST was conducted in a quiet environment with no significant changes in lighting conditions.After each trial, mice were removed from the water and returned to their cages, and the water in the tank was replaced.

| Tail suspension test
TST was also carried out following the previously described method. 59e posterior one-third of the tail of each mouse was taped and suspended approximately 40 cm above the ground for 6 min.Immobility time during the last 4 min was measured.Immobility was defined as a lack of active escape movements and maintaining a vertical position during suspension.To prevent mutual interference between mice during the experiment, opaque black partitions were used to separate individual mice, ensuring they did not come into contact with each other.cDNA synthesis was conducted according to the instructions of the reverse transcription kit (GenStar, China).Quantitative real-time PCR was performed according to the instructions provided with the qPCR kit, utilizing the Genious 2X SYBR Green Fast qPCR Mix (Abclonal, China).GAPDH was used as an internal control.The primers used in qPCR were synthesized by Beijing Genomics Institution.

| Co-immunoprecipitation
Brain tissue collection and protein extraction were the same as western blotting.Co-immunoprecipitation was quantified using a Co-IP kit (abs995, Absin, Shanghai, China) according to the manufacturer's instructions.Initially, 5 μL of Protein A and 5 μL of Protein G were integrated into the 500 μL sample and incubated at 4°C for 60 min, followed by centrifugation at 12,000g for 1 min at 4°C.One microgram of primary antibody (p53, mouse monoclonal antibody, ab26, Abcam, Shanghai, China; or Mouse IgG, A7028, Beyotime; as appropriate) was added to the supernatant and incubated overnight at 4°C with gentle mixing.The samples were then washed with 500 μL wash buffer (1×) and centrifuged at 12,000g for 1 min.Forty microlitres of SDS sample buffer (1×) was added to the precipitate, and the samples were added and incubated in a water bath at 95-100°C for 5 min.Followed by centrifugation at 14,000g for 1-min, primary antibodies p53 (1:800, ab26, mouse monoclonal antibody, Abcam) and Klf4 (1:1000, ab129473, rabbit polyclonal antibody, Abcam, Shanghai, China) were added.

| C-Fos immunofluorescence
Two hours after the PTZ injection, mice were deeply anaesthetised with 65 mg/kg pentobarbital and perfused transcardially with 0.1 M phosphate buffered saline (PBS), followed by 4% paraformaldehyde in PB (pH 7.4).The brains were carefully extracted from the skull and post-fixed with 4% paraformaldehyde for 24 h, followed by 30% sucrose in PBS for 3 days.The HP was sectioned into 15μm coronal slices with a cryostat (Leica CM1860; Leica Microsystems, Germany).
The sections were rinsed in PBS and then blocked by 10% goat serum for 60 min and then rinsed in 0.1 M PBS.Primary c-Fos antibodies (sc253; 1:1000; Santa Cruz Biotechnology) were diluted to 1:1000 and incubated overnight at 4°C on a rotating shaker.Following the three washes with 0.1 M PBS, the sections were incubated in Alexa Fluor 594-conjugated goat anti-rabbit secondary antibody (A11012; 1:1000; Zhongshan) for 1 h at room temperature.Subsequently, the slices were imaged using an Olympus microscope (BX51).

Figures 1 and 2
Figures 1 and 2 show hippocampal protein expression levels of Klf4 after PTZ-induced acute seizure.Klf4 protein expression was significantly increased after a single PTZ administration both in HP (Figure 1A,B: p < 0.01) and PFC (Figure 1C,D: p < 0.01) of mice.PCR results for Klf4 mRNA expression are shown in Figure 2. Klf4 mRNA expression was also significantly increased after single PTZ administration both in HP (Figure 2A: p < 0.01) and PFC (Figure 2B: p < 0.01) of mice.

Figure 4
shows behavioural results in conditional hippocampal Klf4-KO mice compared to wild-type mice.There were no significant behavioural differences between wild-type and conditional hippocampal knockout of Klf4-KO mice in the Y-maze test and open field test (OFT).The only behavioural differences were in the forced swimming test (FST) and F I G U R E 1 Protein expression levels of transcription factors in in acute PTZinduced seizure.(A, B) HP Klf4 protein expression in the acute PTZ-treated mice; (C, D) FC Klf4 protein expression in the acute PTZ-treated mice.PTZ, Pentylenetetrazole (70 mg/kg, ip).Columns represent the mean ± S.E.M. n = 6.**p < 0.01 versus PTZ group.tail suspension test (TST), where immobility time was significantly decreased after conditional hippocampal Klf4-KO (Figure 4C FST: p < 0.05; Figure 4D TST: p < 0.01).

Figure
Figure 5A-F shows the molecular changes after conditional hippocampal Klf4-KO in the HP of mice using a NeuN, a marker of

7
Effects of overexpression of Klf4 on action potential (AP) frequency in hippocampal pyramidal neurons.(A) Visualization of the primary cultured hippocampal neuron.(B) The representative recording shows that action potentials were inhibited by Klf4 overexpression.(C) The mean frequency plots showing changes in AP frequency between groups.Columns represent the mean ± S.E.M. n = 10.*p < 0.05, **p < 0.01, and ***p < 0.001.results may relate to different roles of Klf4 under different conditions.

First, the effects
of Klf4 manipulation were only examined in the HP.Considering the potential impact of Klf4 in different neuronal populations or brain regions, future studies should explore its role in other areas of the brain.Additionally, investigating the function of Klf4 in other seizure models, such as genetic models or chronic epilepsy models, could provide a broader understanding of its role in epilepsy pathophysiology.The specific molecular mechanisms of the | 9 of 14 LI et al.

Figure 8
outlines the timeline and procedures for the experiments.

:
Mice were taken from their home cages and placed individually into Plexiglas cages (25.5 × 15 × 14 cm) after PTZ injection and observed for 30 min.PTZ seizure scale: Stage 0, characterized by no response; Stage 1, exhibiting eating behaviour and facial twitching; Stage 2, displaying myoclonic body jerks; Stage 3, demonstrating forelimb clonus and rearing behaviour; Stage 4, experiencing clonic convulsions and turning onto the side; and Stage 5, showing generalized clonic convulsions and loss

F I G U R E 8 | 11 of 14 LI
Experimental design and procedures.Experimental design and procedures.(A) In vivo study: Behavioral assessment following single PTZ injection and collection of brain tissue.(B) In vivo study: upper: Behavior and molecular characterization of conditional hippocampal Klf4-KO mice; lower: The effect of conditional hippocampal Klf4-KO on PTZ-induced acute seizure mice behavior and brain tissue collection.(C) In vitro study: Electrophysiological recordings from hippocampal neurons.et al.